Controversial D.C. schools Chancellor Michelle A. Rhee will announce her resignation on Wednesday, nearly four years after she was brought in by Mayor Adrian M. Fenty to improve the city's languishing public education system.

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Much of the public discussion about education reform this fall was dominated by the widely anticipated resignation of Chancellor Michelle A. Rhee and presumptive Democratic mayor-elect Vincent C. Gray's willingness to sustain the initiatives she launched. But the survival of Rhee's agenda - especially for hiring, evaluating and firing teachers - will also be determined by those at the top of the 4,000-member union, which spent heavily to unseat her boss, Mayor Adrian M. Fenty (D).

George Parker, who signed the game-changing labor contract with Rhee that was approved by members in June, is running for reelection to a three-year term. Reform advocates hailed the pact for provisions such as performance pay linked to student achievement and new latitude for principals to make hiring decisions.

Parker faces challenges from three veteran teachers who say he gave away too much at the bargaining table, weakening job security and other protections. His opponents, Elizabeth Davis, Christopher Bergfalk and the union's general vice president, Nathan Saunders, also favor abolishing or substantially revising Rhee's signature measure, the IMPACT evaluation system, which can trigger dismissals for teachers with low scores.

Parker said his opponents don't understand the political and cultural climate that now surrounds public education. Unionized teachers need to get in front of the reform movement and assert some leadership, he said, or risk being steamrolled by it. He calls their candidacies a vestige of "old-school unionism."

"We need to become a different kind of union," he told a gathering of teachers earlier this month at Miner Elementary.

The election, which concludes on Wednesday when mail ballots are counted by an independent arbitrator, has been nasty and long. Union bylaws call for the election to have been held in May. But a series of procedural disputes that landed in federal court led the union's national parent organization, the American Federation of Teachers, or AFT, to assume control of the contest.

It has also been marked by internal feuds and charges that Parker attempted to punish Saunders, a political opponent and his most outspoken union critic. The union's executive board, which is friendly to Parker, voted this spring to suspend Saunders's salary and withhold renewal of his annual leave of absence from teaching duties. Parker says that the accusations of retaliation have no merit and that Saunders was sanctioned by the board for failing to perform his duties as general vice president.

The AFT nevertheless ordered the local union to restore Saunders's pay and leave status last month. The executive board has offered to reinstate Saunders, but without back pay. A federal judge dismissed Saunders's challenge to the matter on Friday.

Saunders, 45, ran on a reform ticket with Parker in 2005, after the union was devastated by a financial scandal that sent president Barbara A. Bullock to federal prison as the central figure in the theft of more than $4 million in union funds.

But he now says Parker has been far too passive, presiding over a period in which Rhee disrespected and maligned District teachers.

"The poor treatment union members receive is a result of poor leadership at the top," said Saunders, who teaches U.S. history at H.D. Woodson High School while he attempts to resolve his dispute with Parker and the executive board.